SUMMARY: Strains of and , including mucoid capsulate, mucoid non-capsulate, smooth and rough variant forms, were grown on defined agar media. The polysaccharide content of the cultures was estimated by the anthrone method and related to the amount of growth as measured by the non-dialysable nitrogen content. Polysaccharide production, as measured by the polysaccharide: nitrogen ratio, was increased in all strains when growth was limited by a restricted supply of nitrogen source so that added carbohydrate remained in relative excess. A low incubation temperature, 15–20° instead of 35°, influenced polysaccharide production differently in the various strains and species; thus it greatly increased production in strains, but decreased it in strains grown on certain media. The various strains showed considerable differences in the amount of polysaccharide production and in the distribution of the polysaccharide between the different possible sites of accumulation: i.e. intracellular, capsular and as loose slime. The mucoid strains produced the largest amounts of polysaccharide, most of which was present extracellularly as capsules or slime; the smooth strains produced much smaller amounts, almost entirely intracellular; a rough strain produced least of all. The antigenic constitution of certain strains was examined, particularly that of a mucoid capsulate and mucoid non-capsulate and non-mucoid smooth variants derived from it. The designation of such morphological and immunological variants is discussed.


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